All eyes were on 14-year-old Garry Kasparov when he went into a big think, early in a Caro-Kann Defense, during his first Soviet Championship. It was obvious to his fellow players—and to virtually all of the many spectators—that he was calculating a knight sacrifice, for two pawns and a strong attack.

But 45 minutes later, Kasparov played a quiet move instead. After his game against Vladimir Bagirov ended in a draw at move 30, Mikhail Tal asked him why he didn’t play Nxe6.

“I saw it but I couldn’t calculate it all!” Kasparov exclaimed.

Tal smiled. “Garik, first you sacrifice,” he said softly. “And then you calculate.”

When he retold the story, Tal admitted he was half-joking. But his words underline a problem that you—and every other every improving player—face:

You don’t make the same mistake you made in your first tournaments—that is, you never play a move without considering the consequences. You don’t underthink.

But there’s another pitfall. When you spend too much time on the consequences, you overthink.

Don’t overthink!

Black replied 32. ... Ra8 and Leko could have just nursed his extra pawn towards victory with 33. Rc1 or 33. Rxa8+. But he felt this was one of those critical moments when there might be a knockout blow that saves two hours of tough technique.

Unlike Tal, he took the sensible precaution of calculating as far as he could. Unlike Kasparov, he was able to calculate as far as he wanted.

But then Leko began to second-guess himself. It wasn’t anything in particular that he saw. He just lost confidence in 33. Bxg7+. Instead, he played 33. Rf1? and soon had all but blown the win.

Doubting yourself for no reason is a typical overthinking trap. But there are many others.

One occurs in situations that are simply beyond calculation. If you try to find absolute clarity in a position that is defiantly fuzzy, you’re bound to become frustrated. You usually end up rejecting a good, perhaps great, move.

“I wonder how many delightful combinations I have ruined in my many years of tournament play only because of the fact that I noticed a counter-combination for my opponent,” David Bronstein wrote. This was a mistake, he added, because often the counter-combination would have been unsound—and his opponent didn’t see it anyway.

Overthinking was the downfall of Alexander Khalifman in the 1997 FIDE world championship tournament. He was on the verge of eliminating the favorite, Vishy Anand, when he reached a won endgame. But Khalifman didn’t trust what he saw.

“I looked for a trick in each of his moves and couldn’t believe that he had just missed something,” he said. Khalifman drew that game, lost the next one and it was Anand, not him, who sailed into the championship finals.

A few years later one of his opponents fell into yet another kind of overthinking trap: trying to find a forced win when none exists.

Yefim Geller said world champions like Bobby Fischer, Mikhail Botvinnik, and Tal achieved the “golden mean” of thinking the right amount. Geller was able to beat them on occasion. But he never got close to the title himself because, he admitted, he was a serial overthinker: “I look at masses of variation and lose time and strength.”

That’s why today’s GMs often evaluate a move by two standards. First, whether it’s good or bad. Second, by whether it’s worth the time spent on it.

For example, Boris Gelfand gave one of his moves a “!?” in a 1991 match with Nigel Short. It earned the “exclam” because it was the best move, he said. But it also deserved the question mark because he spent 15 minutes on it, leaving himself with 15 minutes for 13 moves. Even the most efficient thinkers of the last 20 years make those “!?” moves.

White also considered 13. Ndf5 Bc5 14. b4 but quickly spotted a good answer, 14. ... exf5 15. bxc5 Re8!. Yet he still ended up spending 11 minutes—to investigate pretty but irrelevant lines such as 14. ... Bxb4 15. Nxg7! Bc3! 16. N7h5, according to his second Aleksander Nikitin.

13. ... Re8 14. Bb2 b6 15. Nh5 Bb7

This bears a striking resemblance to that Kasparov-Bagirov game ten years before. This time White took five minutes to sac—and that’s remarkable because he had to reject an equally appealing alternative, 16. Nxg7!? Kxg7 17. Qxe6! (by finding a good defense, 17. ... Kh8! 18. Qxf7 Rg8!).

16. Nxe6! fxe6? 17. Qxe6+ Kf8?

Black’s last two moves were more or less forced. Nikitin gave both of them question marks, purely because Black wasted 18 and seven minutes on them. Soon time pressure took its toll on both players.

Now that he’s out of chess, Kasparov offers this advice: “You have to recognize when you are leaving the realm of what can be confirmed beyond a reasonable doubt,” he wrote in How Life Imitates Chess.

In other words, the key to calculating is knowing what you can’t calculate.

See “Looks at Books” in the September 2007 Chess Life, page 12, for a review by Bruce Pandolfini of Kasparov’s How Life Imitates Chess.

First American Chess Congress

This month marks the 150th anniversary of the First American Chess Congress, the ancestor of the U.S. Championship and the event that introduced Paul Morphy to the world. New York 1857 was Morphy’s only tournament but it wasn’t just a collection of Morphy brilliancies. The Congress’ non-Morphy games provide this month’s quiz. In each of the following positions you are asked to find the fastest winning line of play. Usually this will mean the forced win of a decisive amount of material.